When a partner has been unfaithful
The suttas treat this as harm; the precept on sexual conduct is argued from exactly the pain you are in — no one wants this done to them. They also give five specific ways to put down resentment without pretending nothing happened. The images that replay at night add their own weight to a hurt that is already real. What the canon does not do is tell you whether to stay, forgive, or leave, and whether trust can be rebuilt is for the two of you and perhaps a counsellor. If you are afraid of your partner, a domestic violence line can help you make a plan — in the US, call 1-800-799-7233; elsewhere, findahelpline.com lists local services. If you are afraid of your own anger, tell a counsellor or your doctor this week. If anyone is in immediate danger, call your local emergency number.
What the suttas say
“Mendicants, a mendicant should use these five ways to completely get rid of resentment when it has arisen toward anyone. What five? You should develop love for an individual you resent. That’s how to get rid of resentment for that individual. You should develop compassion for an individual you resent. … You should develop equanimity for an individual you resent. … You should disregard an individual you resent, paying no attention to them. … You should focus on the ownership of deeds regarding that individual: ‘This venerable is the owner of their deeds and heir to their deeds. Deeds are their womb, their relative, and their refuge. They shall be the heir of whatever deeds they do, whether good or bad.’ That’s how to get rid of resentment for that individual. A mendicant should use these five ways to completely get rid of resentment when it has arisen toward anyone.”
A practical list — love, compassion, equanimity, not attending, reflecting on kamma.
Where this stops: Reflecting that people own their deeds is never a way to call someone's misfortune their kamma, and putting down resentment is never a reason to stay near someone who keeps doing harm.
AN 5.161:1.1–1.15 · Getting Rid of Resentment (1st)
“Pañcime, bhikkhave, āghātapaṭivinayā yattha bhikkhuno uppanno āghāto sabbaso paṭivinetabbo. Katame pañca? Yasmiṁ, bhikkhave, puggale āghāto jāyetha, mettā tasmiṁ puggale bhāvetabbā; evaṁ tasmiṁ puggale āghāto paṭivinetabbo. Yasmiṁ, bhikkhave, puggale āghāto jāyetha, karuṇā tasmiṁ puggale bhāvetabbā; evaṁ tasmiṁ puggale āghāto paṭivinetabbo. Yasmiṁ, bhikkhave, puggale āghāto jāyetha, upekkhā tasmiṁ puggale bhāvetabbā; evaṁ tasmiṁ puggale āghāto paṭivinetabbo. Yasmiṁ, bhikkhave, puggale āghāto jāyetha, asatiamanasikāro tasmiṁ puggale āpajjitabbo; evaṁ tasmiṁ puggale āghāto paṭivinetabbo. Yasmiṁ, bhikkhave, puggale āghāto jāyetha, kammassakatā tasmiṁ puggale adhiṭṭhātabbā: ‘kammassako ayamāyasmā kammadāyādo kammayoni kammabandhu kammapaṭisaraṇo, yaṁ kammaṁ karissati kalyāṇaṁ vā pāpakaṁ vā tassa dāyādo bhavissatī’ti; evaṁ tasmiṁ puggale āghāto paṭivinetabbo. Ime kho, bhikkhave, pañca āghātapaṭivinayā, yattha bhikkhuno uppanno āghāto sabbaso paṭivinetabbo”ti.
Furthermore, a noble disciple reflects: ‘If someone were to have relations with my wives, I wouldn’t like it. But if I were to have relations with someone else’s wives, he wouldn’t like that either. The thing that is disliked by me is also disliked by others. Since I dislike this thing, how can I inflict it on others?’
The precept on sexual conduct argued the same way — from how it would feel to be on the other side.
Where this stops: Spoken to men of a society with several wives to a household; what carries is the question it asks, not the household it assumes.
SN 55.7:6.1–6.5 · The People of Bamboo Gate
Puna caparaṁ, gahapatayo, ariyasāvako iti paṭisañcikkhati: ‘yo kho me dāresu cārittaṁ āpajjeyya, na metaṁ assa piyaṁ manāpaṁ. Ahañceva kho pana parassa dāresu cārittaṁ āpajjeyyaṁ, parassapi taṁ assa appiyaṁ amanāpaṁ. Yo kho myāyaṁ dhammo appiyo amanāpo, parassa peso dhammo appiyo amanāpo. Yo kho myāyaṁ dhammo appiyo amanāpo, kathāhaṁ paraṁ tena saṁyojeyyan’ti.
“Do you then serve them with fresh and cooked foods and savories?” “Sometimes I do.” “But if they don’t accept it, brahmin, who does it belong to?” “In that case it still belongs to me.” In the same way, brahmin, when you abuse, harass, and attack us who do not abuse, harass, and attack, we don’t accept it. It still belongs to you, brahmin, it still belongs to you! Someone who, when abused, harassed, and attacked, abuses, harasses, and attacks in return is said to eat the food and have a reaction to it. But we neither eat your food nor do we have a reaction to it.
Declining to take in what someone hurls at you in anger, the way a guest can leave a dish untouched.
Where this stops: Concerns how abuse is received inwardly; it is no reason to stay where someone keeps abusing you.
SN 7.2:2.5–3.2 · With Bhāradvāja the Rude
“Taṁ kiṁ maññasi, brāhmaṇa, api nu tesaṁ anuppadesi khādanīyaṁ vā bhojanīyaṁ vā sāyanīyaṁ vā”ti? “Appekadā nesāhaṁ, bho gotama, anuppademi khādanīyaṁ vā bhojanīyaṁ vā sāyanīyaṁ vā”ti. “Sace kho pana te, brāhmaṇa, nappaṭiggaṇhanti, kassa taṁ hotī”ti? “Sace te, bho gotama, nappaṭiggaṇhanti, amhākameva taṁ hotī”ti. Evameva kho, brāhmaṇa, yaṁ tvaṁ amhe anakkosante akkosasi, arosente rosesi, abhaṇḍante bhaṇḍasi, taṁ te mayaṁ nappaṭiggaṇhāma. Tavevetaṁ, brāhmaṇa, hoti; tavevetaṁ, brāhmaṇa, hoti. Yo kho, brāhmaṇa, akkosantaṁ paccakkosati, rosentaṁ paṭiroseti, bhaṇḍantaṁ paṭibhaṇḍati, ayaṁ vuccati, brāhmaṇa, sambhuñjati vītiharatīti. Te mayaṁ tayā neva sambhuñjāma na vītiharāma.
Mendicants, these seven things that please and assist an enemy happen to an irritable woman or man. What seven? Firstly, an enemy wishes for an enemy: ‘If only they’d become ugly!’ Why is that? Because an enemy doesn’t like to have a beautiful enemy. An irritable individual, overcome and overwhelmed by anger, is ugly, even though they’re nicely bathed and anointed, with hair and beard dressed, and wearing white clothes. This is the first thing that pleases and assists an enemy which happens to an irritable woman or man.
One cost of anger shown plainly, framed as doing an enemy's work for them; useful when someone feels their anger is justified.
Where this stops: Only the frame and the first of the seven are in this range; do not cite the other six from it. Looking ugly is how the sutta says anger shows, not a judgement of anyone's appearance.
AN 7.64:1.1–1.9 · Irritable
Sattime, bhikkhave, dhammā sapattakantā sapattakaraṇā kodhanaṁ āgacchanti itthiṁ vā purisaṁ vā. Katame satta? Idha, bhikkhave, sapatto sapattassa evaṁ icchati: ‘aho vatāyaṁ dubbaṇṇo assā’ti. Taṁ kissa hetu? Na, bhikkhave, sapatto sapattassa vaṇṇavatāya nandati. Kodhanoyaṁ, bhikkhave, purisapuggalo kodhābhibhūto kodhapareto, kiñcāpi so hoti sunhāto suvilitto kappitakesamassu odātavatthavasano; atha kho so dubbaṇṇova hoti kodhābhibhūto. Ayaṁ, bhikkhave, paṭhamo dhammo sapattakanto sapattakaraṇo kodhanaṁ āgacchati itthiṁ vā purisaṁ vā.
Householders, if wife and husband want to see each other in both this life and the next, they should be equals in faith, ethics, generosity, and wisdom.
Nakula's parents — the Buddha's picture of a good partnership.
Where this stops: A picture of a partnership both people want; not a standard to measure a partner who broke faith against, and not a reason to stay.
AN 4.55:3.1 · Equality (1st)
Ākaṅkheyyuñce, gahapatayo, ubho jānipatayo diṭṭhe ceva dhamme aññamaññaṁ passituṁ abhisamparāyañca aññamaññaṁ passituṁ ubhova assu samasaddhā samasīlā samacāgā samapaññā, te diṭṭhe ceva dhamme aññamaññaṁ passanti abhisamparāyañca aññamaññaṁ passantīti.